Magnetic recording medium, method of fabricating magnetic recording medium, and magnetic storage

ABSTRACT

A magnetic recording medium having first undercoating layers  40, 40 ′ formed directly or via substrate face undercoating layers on a substrate  40 , second undercoating layers  42, 42 ′ directly formed on the first undercoating layers  40, 40 ′, magnetic films  43, 43 ′ formed on the second undercoating layers  42, 42 ′, and protective films  44, 44 ′ formed on the magnetic films  43, 43 ′. Clusters having a large amount of oxygen are dispersed on the boundary face of the first and second undercoating layers. Preferably, the first undercoating layer is made of an alloy which includes two kinds of elements in which the difference between oxide formation standard free energies ΔG° of the elements at the temperature of 250° C. is large.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a magnetic storage used for anauxiliary storage of a computer, or the like, a magnetic recordingmedium used for the magnetic storage, and a method of fabricating themagnetic recording medium.

[0002] With progress of information-oriented society, the amount ofinformation daily used is steadily increasing. Demand for high densityrecording and large memory capacity for a magnetic storage isaccordingly being stronger. An inductive head using voltage change inassociation with magnetic flux change with time is used as aconventional magnetic head. Both of recording and reproduction areperformed by one head. In recent years, a composite head having a headfor recording and a head for reproduction, in which an MR (magneticresistive) head with higher sensitivity is used as the reproductionhead, is rapidly increasingly used. In the MR head, change in electricresistance of a head device in association with change in magnetic fluxleaked from a magnetic recording medium is used. A head with highersensitivity using a very large magnetic resistive change (giant magneticresistive effect or spin valve effect) which occurs in a plurality ofmagnetic layers laminated via non-magnetic layers is being developed.According to the head, change in electric resistance which is caused bychange in relative directions of magnetization of the plurality ofmagnetic layers via the non-magnetic layers by the magnetic field leakedfrom a medium is used.

[0003] In magnetic recording media which are practically used atpresent, alloys containing Co as a main component, such as Co—Cr—Pt,Co—Cr—Ta, Co—Ni—Cr, and the like are used for a magnetic layer. Each ofthe Co alloys has a hexagonal close-packed (hcp) structure in which ac-axis direction is an easy axis of magnetization, so that a crystalorientation such that the c-axis of the Co alloy is the longitudinaldirection, that is, (11.0) orientation is desirable as a longitudinalmagnetic recording medium for reversing the magnetization in themagnetic layer and recording. The (11.0) orientation is, however,unstable, so that when the Co alloy is formed directly on a substrate,such an orientation is not generally obtained.

[0004] A method in which the fact that a Cr (100) plane having abody-centered cubic (bcc) structure has good lattice matching with a Co(11.0) plane is used, a (100) orientated Cr undercoating layer is firstformed on a substrate, and a Co alloy magnetic film is epitaxiallygrown, thereby obtaining the (11.0) orientation such that the c-axis ofthe Co alloy magnetic film is orientated to the in-plane direction.Also, a method in which a second element is added to Cr to improve thecrystal lattice matching performance in the boundary face between the Coalloy magnetic film and the Cr undercoating layer and intervals oflattices in the Cr undercoating layer are widened is used. The Co (11.0)orientation is further improved and coercive force can be increased.There are examples of adding V, Ti, and the like.

[0005] Another factor necessary to realize high recording density isreduction in noises as well as increase in coercive force of themagnetic recording medium. Since the MR head has extremely highreproduction sensitivity, it is suitable for high density recording.However, the MR head is sensitive not only to reproduction signals fromthe magnetic recording medium but also to noises. Consequently, in themagnetic recording medium, it is requested to reduce noises more than aconventional technique. It is known that in order to reduce the mediumnoise, it is effective to fine and uniform the grain size of themagnetic film or the like.

[0006] As an importance request for the magnetic disk medium,improvement in shock resistance can be mentioned. Especially, a magneticdisk apparatus is mounted on a portable information device such as anotebook-sized personal computer or the like in recent years, so thatimprovement in the shock resistance is very important subject from theviewpoint of improving reliability. A glass substrate whose surface isstrengthened or a crystallized glass substrate is used in place of aconventional Al alloy substrate to which Ni—P is plated on the surface,thereby enabling the shock resistance of the magnetic disk medium to beimproved. Since the surface of the glass substrate is smoother than thatof the conventional Ni—P plated Al alloy substrate, it is advantageousto reduce floating spacing between a magnetic head and the magneticrecording medium and is suitable to obtain high recording density. Incase of using the glass substrate, however, problems of poor adhesionwith the substrate, invasion of impurity ion from the substrate orabsorption gas on the surface of the substrate into the Cr alloyundercoating layer, and the like occur. As a countermeasure, any ofvarious metal films, alloy films, oxide films is formed between theglass substrate and the Cr alloy undercoating layer.

[0007] Japanese Patent Application Laid-Open Nos. 62-293511, 2-29923,5-135343, and the like are techniques related to the above.

[0008] It is known that, as mentioned above, reducing and uniforming thegrain size of the magnetic film is effective to reduce the medium noise.However, when a magnetic disk apparatus was produced experimentally bycombining a magnetic recording medium with a recording density of about900 megabits per square inch and a high-sensitive MR head according tothe conventional technique, sufficient electromagnetic conversioncharacteristic by which 1 gigabit or higher recording density per squareinch can be obtained could not be obtained. Especially, when the glasssubstrate was used as a substrate of the magnetic recording medium, poorelectromagnetic conversion characteristic in a high recording densityarea was resulted. The cause was examined and it was found that the Cralloy undercoating layer formed directly or via various metal or alloysas used in the conventional techniques on the glass substrate was notorientated as strong (100) as that in the case where it was formed onthe Ni—P plated Al alloy substrate. A crystal plane except for (11.0) ofthe Co alloy magnetic film is grown in parallel to the substrate and thein-plane orientation of the c-axis as an easy axis of magnetization wassmall. Thus, the coercive force was reduced and a reproduction outputwith the high density recording deteriorated. In the case of using theglass substrate, the grain in the magnetic film was larger than that ofthe Al alloy substrate and the distribution of grains was larger by 20to 30%. The medium noise was therefore increased and the electromagneticconversion characteristic deteriorated. Even if an amorphous film or afine crystal film disclosed in Japanese Patent Application Laid-Open No.4-153910 was formed between the glass substrate and the undercoatinglayer, the size of the grain in the magnetic film was sometimes reducedto a certain degree but was not sufficiently reduced. It was noteffective with respect to the reduction in the grain distribution, andpreferable electromagnetic conversion characteristic could not beobtained.

SUMMARY OF THE INVENTION

[0009] It is a first object of the invention to provide a magneticrecording medium having low noise level in which orientation of amagnetic film is improved and the grains in the magnetic film are finedand uniformed.

[0010] It is a second object of the invention to provide a method offabricating the magnetic recording medium.

[0011] It is a third object of the invention to provide a magneticstorage with high recording density.

[0012] In order to achieve the first object, according to a magneticrecording medium of the invention, a first undercoating layer isdeposited directly or via a third undercoating layer on a substrate, asecond undercoating layer is directly deposited on the firstundercoating layer, and a magnetic film is deposited on the secondundercoating layer. Clusters having a large amount of oxygen are spreadon the boundary face of the first and second undercoating layers.

[0013] In order to achieve the second object, according to a method offabricating a magnetic recording medium of the invention, a firstundercoating layer is formed on a substrate directly or via a thirdundercoating layer and is exposed to an atmosphere including oxygen fora time period that PO₂·t (where, PO₂·t is oxygen partial pressure of theatmosphere and t is time of exposure of the substrate to the atmosphere)is in a range from 1×10⁻⁶ (Torr-sec) to 1×10⁻² (Torr-sec), a secondundercoating layer is directly formed on the first undercoating layerexposed to the atmosphere, and a magnetic film is formed on the secondundercoating layer.

[0014] In order to achieve the third object, a magnetic storage of theinvention comprises: the above-mentioned magnetic recording medium; amagnetic head constructed by a recording part and a reproducing partprovided in correspondence to the faces of the magnetic recordingmedium; a drive unit for changing relative positions of the magneticrecording medium and the magnetic head; a magnetic head driving unit forpositioning the magnetic head to a desired position; and a recording andreproduction signal processing system for inputting signals to themagnetic head and reproducing output signals form the magnetic head.

[0015] It is preferable that the first undercoating layer is made of analloy consisting of two or more kinds of elements. In the case whereelements which oxidize differently are included in the alloy and thefirst undercoating layer is exposed to an atmosphere at a certain oxygenpartial pressure for a certain time, it is estimated as follows. Auniform oxide film whose surface is continuous in the plane is notformed but clusters having a large amount of oxygen are locally formedin an area rich in the element which is easily oxidized and become thenucleation of the second undercoating layer. The grains of the secondundercoating layer grown on the clusters are fined and uniformed andfurther, the average gain size of the magnetic film is reduced and thegrain diameter is uniformed.

[0016] The magnetic recording medium of the invention has effects onreduction in medium noise, increase in coercive force, and the like.According to the method of fabricating the magnetic recording medium ofthe invention, the above magnetic recording medium can be easilyfabricated. The magnetic storage of the invention using the magneticrecording medium has high recording density. Providing of oxidizing stepin a process sequence of fabricating a magnetic disc is known by U.S.Pat. No. 4,552,820.

[0017] The purpose of oxidation in the invention is to reduce amodulation of reproduction output. The modulation is a kind offluctuation in reproduction output due to anisotropy of crystalstructure occurring in a sputtering apparatus of an in-line type (methodof depositing films while conveying, that is, moving a substrate in onedirection). Since a sputtering apparatus of a stationary facing type(method of depositing films while a substrate and a target stationarilyface each other) is mainly used at present, the problem is ignored. Evenin the sputtering apparatus of the in-line type, since a film thicknessof an undercoating layer and that of a magnetic layer are reduced as therecording density becomes higher, the problem of the modulation issmall. The present invention intends to reduce noise by uniforming theorientation of the crystal and is different from the above U.S. patent.According to the above U.S. patent, by oxidizing an Ni—V layer beforedepositing a Cr layer as an undercoating layer, the grain size of the Crfilm is increased, thereby reducing the modulation. On the contrary,according to the present invention, clusters are generated byoxidization in a step prior to formation of the Cr alloy undercoatinglayer, and the grain size of the Cr alloy undercoating layer is reduced,thereby realizing reduction in noise.

[0018] The above and other objects and features of the present inventionwill become more apparent from the following detailed description ofembodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic cross section of a magnetic recording mediumaccording to an embodiment of the invention;

[0020]FIG. 2 is a schematic diagram showing an example of a layerforming device of a magnetic recording medium of the invention;

[0021]FIG. 3 is a diagram showing the relation of the product ofactivation volume and magnetic moment with respect to conditions at thetime of forming a multi- undercoating layer of the magnetic recordingmedium of the invention;

[0022]FIG. 4 is a schematic diagram of a TEM photograph of clustersformed on a first undercoating layer of the magnetic recording medium ofthe invention;

[0023]FIG. 5 is a diagram showing X-ray diffraction patterns of amagnetic recording medium according to an embodiment of the inventionand a magnetic recording medium according to a comparison example;

[0024]FIGS. 6a and 6 b are a plan schematic diagram and a schematiccross section according to an embodiment of a magnetic storage of theinvention, respectively; and

[0025]FIG. 7 is a schematic cross section of a magnetic recording mediumaccording to another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026]FIG. 1 is a schematical cross section of a representativeembodiment of a magnetic recording medium according to the invention.

[0027] On both of the faces of a substrate 40 made of a strengthenedglass, first undercoating layers 41, 41′, second undercoating layers 42,42′, magnetic films 43, 43′, protective films 44, 44′, and lubricantfilms 45, 45′ are sequentially laminated in this order, respectively.

[0028]FIG. 2 is a schematic diagram showing an example of a sputteringapparatus of a single disc process type for fabricating the magneticrecording medium of FIG. 1. In the actual sputtering apparatus, a mainchamber 29 is positioned in the center and a preparation chamber 21, afirst undercoating layer forming chamber 22, a heating chamber 23, anoxidation chamber 24, a second undercoating layer forming chamber 25, amagnetic layer forming chamber 26, protective film forming chambers 27a, 27 b, 27 c, 27 d, and a take-out chamber 28 are arranged in acircular shape around the main chamber 29. An operation for feeding thesubstrate after processing in a certain chamber to the next chamber issimultaneously performed with respect to the respective chambers. Thatis, a plurality of substrates can be simultaneously processed in thesputtering apparatus and the substrates can be sent sequentially to thechambers. Since it is preferable to form the protective film at lowspeed, the four protective film forming chambers 27 a, 27 b, 27 c, and27 d are provided and ¼of a desired thickness is formed in each chamber.

[0029] In the sputtering apparatus, the substrate 20 made ofstrengthened glass is first introduced to the preparation chamber 21 andthe preparation chamber 21 is vacuumized, sequentially transferred tothe chambers via the main chamber 29, and processed as follows. Forexample, an alloy of 60 at %Co-30 at% Cr-10 at%Zr is formed as a firstundercoating layer at a room temperature and is heated to 270° C., andafter that, it is exposed to a mixed gas of argon and oxygen in theoxidation chamber 24. At this time, the mixing ratio of the mixed gasand the time to expose to the atmosphere of the mixed gas are variablychanged. The second undercoating layer made of, for example, an alloy of75 at %Cr-15 at %Ti and the magnetic layer made of, for example, analloy of 75 at %Co-19 at %Cr-6 at %Pt are sequentially laminated. Duringthis period, the temperature is kept at or slightly lower than 270° C.Further, carbon having thickness of 10 to 30 nm is formed as theprotective layer.

[0030] When the mixing ratio of the mixed gas and the exposure time tothe mixed gas were changed, it is found that, as shown in FIG. 3, theproduct (v·Isb) of the activation volume v and the magnetic moment Isbshowing a linear correlation with medium noise was extremely small withrespect to the product (PO₂·t) of oxygen partial pressure PO₂ of theatmosphere and exposure time t to the atmosphere. v·Isb is described in“Journal of Magnetism and Magnetic Materials”, Vol. 145, pp. 255 to 260(1995). v·Isb is a quantity corresponding to the minimum unit of themagnetization inversion and the smaller v·Isb is, the smaller the mediumnoise is. Since v·Isb is physical quantity, the medium noise can beobjectively compared irrespective of the recording and reproducingconditions. PO₂·t when v·Isb is the minimum varies according to thecomposite of an alloy of the first or second undercoating layer and thecomposition ratio. According to various experiments, when PO₂·t rangesfrom 1×10⁻⁶ (Torr-sec) to 1×10⁻² (Torr·sec), there was an effect onreduction of the medium noise. Especially, in the case where Co isincluded in the first undercoating layer, it was effective when PO₂·tranges from 1×10⁻⁶ (Torr-sec) to 1×10⁻³ (Torr·sec). That is, it wasconfirmed by using a TEM (transmission electron microscope) that thegrain size of the second undercoating layer was reduced in the region ofPO₂·t where v·Isb is reduced.

[0031] Further, a lubricating film made of absorb 5perfluoroalkylpolyether or the like is deposited to a thickness on theorder of 1 to 10 nm on the protective layer, thereby obtaining areliable magnetic recording medium which can perform high densityrecording.

[0032] Similar effects can be derived when the heat treatment isperformed before the formation of the first undercoating layers 41, 41′.It is also possible that the process is performed at a room temperatureuntil the oxidation, then the temperature is increased to 270° C., andthe second undercoating layer is formed. The heat treatment is a generalmethod of improving the crystallinity of the undercoating layer,enhancing the coercive force of the magnetic film, and reducing thenoise. Usually, the heat treatment is performed about at 200 to 300° C.

[0033] When a carbon film in which hydrogen is added, a film made of acompound of silicon carbide, tungsten carbide, or the like, or acomposite film of the compound and carbon is used as each of theprotective layers 44, 44′, it is preferable since sliding resistance andcorrosion resistance can be improved. After the protective layers areformed, when minute roughness is formed on the surface by performingplasma etching using a fine mask or the like, projections of differentphases are formed on the surfaces of the protective layers by using atarget of compound or mixture, or roughness is formed on the surface byheat treatment, contact area of the head and the medium can be reduced.It is preferable since a problem that the head is stuck to the mediumsurface at the time of a CSS (head contact start and stop) operation canbe avoided.

[0034] In the case of using the Ni—P plated Al alloy substrate as thesubstrate 40 as well, in a manner similar to the case of using the glasssubstrate, the effect that the grains in the magnetic layer are finedwas confirmed.

[0035] Further, in case of using the Al alloy substrate as the substrate40, as shown in FIG. 7, it is preferable that substrate faceundercoating layers 40-1, 40-1′ made of Ni—P or the like are formedbetween the substrate 40 and the first undercoating layers 41, 41′,respectively. Similarly, in case of using the glass substrate as thesubstrate 40 as well, it is preferable that the substrate faceundercoating layers made of any of various metal layers, the alloy film,and the oxide film which are usually used are formed between thesubstrate 40 and the first undercoating layers 41, 41′, respectively.

[0036]FIG. 4 is a schematic diagram illustrating clusters formed on eachof the first undercoating layers 41, 41′. The diagram shows thestructure of a sample of clusters formed on the substrate obtained byforming a single layer of 68 at %Co-24 at %Cr-8 at %W alloy as the firstundercoating layer on the glass substrate when it is seen by using thetransmission electron microscope (TEM). The clusters are minute grainsas shown in FIG. 4 and are uniformly dispersed at intervals of few nm.Standard free energy for oxide formation is used as an index of theoxidizable degree of an element. It is preferable that an alloy formingthe first undercoating layer includes two or more kinds of elements inwhich the difference of the oxide formation standard free energies ΔG°at the temperature of 250° C. is more than 150 (kJ/mol O₂) (in case ofan element in which two or more kinds of oxides exist, (for example, Fehas oxides Fe₂O₃, Fe₃O₄, and the like), the lowest ΔG° is chosen). It ismore preferable to include two or more kinds of elements in which thedifference is 180 (kJ/mol O₂) or more. It is most preferable to includetwo or more kinds of elements in which the difference is 200 (kJ/mol O₂)or more. Although there is no upper limit of the difference, there aregenerally about 1000 combinations.

[0037] When an element whose oxide formation standard free energy ΔG° is−750 (kJ/mol O₂) or lower is included in the alloy, the effect can bederived with a supply of a small amount of oxygen. Table 1 shows variouselements, corresponding oxides, and formation standard free energies ΔG°at the temperature of 250° C. ΔG° is a value read from the diagram ofthe relation between ΔG° and the temperature shown by Coughlin. This isshown in “Refining of nonferrous metals” (new system metal new editionrefining metal version), The Japan Institute of Metals Publisher, 1964,pp.291 to 292. TABLE 1 Element oxide standard free energy for oxideformation Element Oxide ΔG° (kJ/molO₂) Co CoO −398 Mo MoO₃ −410 W WO₃−473 Cr Cr₂O₃ −666 Ta Ta₂O₅ −724 V V₂O₃ −737 Si SiO₂ −783 Ti TiO −933 ZrZrO₂ −992 Al Al₂O₃ −1005 

[0038] As an alloy used for the first undercoating layer, an alloyincluding Cr and at least one kind of element selected from a group ofMo, Ti, Zr and Al is preferable from the viewpoint of adheringperformance to the substrate. Further, when an alloy containing Co andat least one kind of element selected from a group of Cr, Si, V, Ta, Ti,Zr, Al, and W is used as an alloy for the first undercoating layer, thealloy easily becomes amorphous or fine crystal and the texture becomesdense. It is consequently effective when the glass substrate is usedsince the alloy serves as a diffusing barrier against impurities such asalkali element or the like entering from the glass into the layer.Further, it is also effective to use an alloy containing Ni and at leastone kind of element selected from a group of Cr, Si, V, Ta, Ti, Zr, Al,and W for the first undercoating layer, since the alloy easily becomesamorphous or fine crystal. “Amorphous” denotes that a clear peak by theX-ray diffraction is not observed or that a clear diffraction spot and adiffraction ring by the electron beam diffraction are not observed and ahalo-shaped diffraction ring is observed. The fine crystal isconstructed by crystal grains each having the size smaller than that ofthe grain size of the magnetic layer and, preferably, having the averagediameter of 8 nm or smaller. Since the percentage content of an elementhaving the smallest standard free energy ΔG° for oxide formation amongthe alloys used for the first undercoating layer is related to thenumber of nucleation, the percentage content of about 5 at % to 50 at%is preferable since it is effective on reduction of the grain size ofthe second undercoating layer. It is more preferable that it ranges from5 at % to 30 at %.

[0039] Third undercoating layers can be also arranged between the firstundercoating layers 41, 41′ and the substrate 40. For example, the glasssubstrate is used as the substrate 40, various metal layers, alloylayers, oxide layers, or the like shown in the conventional techniquecan be used as the third undercoating layers.

[0040] For the second undercoating layers 42, 42′, it is preferable touse an alloy having the bcc structure such as the Cr alloy having goodlattice matching with the Co alloy magnetic layer. For example, Cr, andCr alloys, that is, CrTi, CrV, CrMo, and the like can be used.

[0041] It is preferable that the thickness of the first undercoatinglayer ranges from 20 to 50 nm and that the thickness of the secondundercoating layer ranges from 10 to 50 nm.

[0042] Preferably, as the magnetic layers 43, 43′, magnetic layers inwhich magnetic anisotropy is oriented toward the in-plane is used. Forsuch a magnetic layer, alloys containing Co as a main component, forexample, Co—Cr—Pt, Co—Cr—Pt—Ta, Co—Cr—Pt—Ti, Co—Cr—Ta, Co—Ni—Cr, and thelike can be used. However, in order to obtain higher coercive force, itis preferable to use the Co alloy including Pt. Further, the magneticlayer can be also constructed by a plurality of layers in whichnon-magnetic interlayers are included.

[0043] As magnetic characteristics of the magnetic layer, it ispreferable that the coercive force measured by applying the magneticfield toward the inside of the film plane is set to 1.8 kilo oersted ormore and the product Br·t of a residual magnetic flux density Brmeasured by applying the magnetic field to the inside of the film planeand the film thickness t ranging from. 20 to 140 gauss micron,preferable recording and reproducing characteristics can be obtained inan area of a recording density of 1 giga bit per one square inch. If thecoercive force is less than 1.8 kilo oersted, it is not preferable sincean output at the time of high recording density (200 kFCI or higher) isreduced. FCI (flux reversal per inch) denotes a unit of recordingdensity. When Br·t is larger than 140 gauss micron, the reproductionoutput at the time of the high recording density is reduced and when itis less than 20 gauss micron, it is not preferable that the reproductionoutput at the time of the low recording density is small.

[0044] When the magnetic film is constructed by a plurality of layershaving non-magnetic interlayers, the film thickness t of the magneticfilm in the calculation of Br-t shows the total of the thickness of themagnetic layers.

[0045] <Embodiment 1>

[0046] In the first embodiment, chemically strengthened soda-lime glassof 2.5 inches is used for the substrate 40. The first undercoatinglayers 41, 41′ made of an alloy of 60 at %Co-30 at %Cr-10 at %Zr eachhaving the thickness of 25 nm, the second undercoating layers 42, madeof a 85 at %Cr-15 at %Ti alloy each having the thickness of 20 nm, themagnetic films 43, 43′ made of a 75 at %Co-19 at %Cr-6 at %Pt alloy eachhaving the thickness of 20 nm, and further the carbon protective layers44, 44′ each having the thickness of 10 nm are sequentially formed onthe faces of the substrate 40, respectively. Single disc processing typesputtering apparatus mdp250A manufactured by Intevac, Inc. is used as alayer forming apparatus and the layers are formed in 10 seconds pertact. Tact denotes a period of time during which the substrate is sentfrom a previous chamber to a certain chamber, processed in the chamber,and sent to a next chamber in the sputtering apparatus. The chamberconstruction of the sputtering apparatus is as shown in FIG. 2. Argon(Ar) gas pressure at the time of depositing the films is fixed to 6mTorr. The oxygen partial pressure in the main chamber 29 during thelayer forming operation is about 1×10⁻⁸ (Torr).

[0047] The first undercoating layers 41, 41′ are deposited in the firstundercoating layer forming chamber 22 in a state where the substrate 4is not heated, heated to 270° C. by a lamp heater in the heating chamber23, and exposed to an atmosphere in which a pressure of 99 %Ar-1 %O₂mixed gas is 5 mTorr (gas flow rate of 10 sccm) for three seconds in theoxidation chamber 24, and the layers are sequentially deposited on theprocessed first undercoating layers 41, 41′ in the second undercoatinglayer forming chamber 25, the magnetic layer forming chamber 26, and theprotective film forming chambers 27 a, 27 b, 27 c, and 27 d. PO₂·t inthis case corresponds to 5 mTorr×0.01×3 seconds=1.5×10⁻⁴ (Torr·sec).After forming the carbon protective films, a material obtained bydiluting a perfluoroalkylpolether material with a fluorocarbon materialis applied as the lubricant films 45, 45′.

<COMPARISON EXAMPLE 1>

[0048] Comparison example 1 relates to a magnetic recording mediumfabricated under the same conditions as the embodiment 1 except that themixed gas is not introduced into the oxidation chamber 24. The coerciveforce of the magnetic recording medium of the embodiment 1 was 2,170oersted which is higher than that of the magnetic recording medium ofthe comparison example 1 by about 300 oersted. The product Br·t of theresidual magnetic flux density Br and the magnetic film thickness t ofthe embodiment 1 was 89 gauss micron. v·Isb of the magnetic recordingmedium of the embodiment 1 was 1.05×10⁻¹⁵ (emu) which is reduced to 47%of 2.24×10⁻¹⁵ (emu) of the magnetic recording medium of the comparisonexample 1, so that the medium noise was reduced to almost the half ofthat of the comparison example 1. The reproduction outputs in theevaluated recording density region of the embodiment 1 and thecomparison example 1 were almost the same. The S/N ratio of the mediumwas improved by an amount corresponding to the reduction of the mediumnoise.

[0049] When the magnetic recording media of the embodiment 1 and thecomparison example 1 were actually inserted into a magnetic diskapparatus and recording and reproduction characteristics by an MR headwere evaluated under that conditions of the track recording density of161 kBPI (bit per inch) and the track density of 9.3 kTPI (track perinch). The magnetic recording medium of the embodiment 1 has an S/Nratio higher than that of the comparison example by 1.8 times andsufficiently satisfied the apparatus specification of 1.6 gigabits persquare inch of the plane recording density. On the other hand, themedium of the comparison example 1 had an insufficient S/N ratio andcould not satisfy the apparatus specification.

[0050] The first undercoating layer made of Co—Cr—Zr alloy is depositedso as to have thickness of 25 nm on the glass substrate and is processedin the oxidation chamber under the same conditions as those in theembodiment 1. When the structure of the Co—Cr—Zr alloy film was examinedby using the TEM (transmission electron microscope), shading reflectingminute clusters corresponding to local oxidation on the surface of thefirst undercoating layer was observed in a TEM image. The diameter ofeach cluster is a few nm and the clusters are almost uniformly formed atpitches of a few nm. The TEM image is schematically shown in FIG. 4.

[0051] When the X-ray diffractions of the magnetic recording media ofthe embodiment 1 and the comparison example 1 were measured, thediffraction patterns shown in FIG. 5 were obtained. When a single firstundercoating layer of Co—Cr—Zr alloy is formed so as to have thethickness of 50 nm on the glass substrate under the same conditions andthe X-ray diffraction was measured, a clear diffraction peak was notseen. In the diffraction pattern of the magnetic recording medium of thecomparison example 1, the CrTi (110) peak of the body-centered cubic(bcc) structure of the second undercoating layer overlaps with theCoCrPt (00.2) peak of the hexagonal close-packed (hcp) structure of themagnetic film and both of them cannot be identified. However, in anycase, the second undercoating layer is not so strongly (100) oriented asthe first magnetic recording medium of the embodiment 1 and has mixedphases of a plurality of crystal grains having different orientations.Consequently, in the Co—Cr—Pt alloy crystal in the magnetic film,crystals are variably oriented and a plurality of diffraction peaks areseen in the Co—Cr—Pt magnetic film.

[0052] On the other hand, in the magnetic recording medium of theembodiment 1, since no diffraction peak is shown in the Co—Cr—Zr alloysingle layer of the first undercoating layer as mentioned above, thediffraction peaks in the diagram are the CrTi (200) peak of the bccstructure of the second undercoating layer and the CoCrPt (11.0) peak ofthe hcp structure of the Co—Cr—Pt magnetic film. It is understood fromthe above that the Cr—Ti alloy of the second undercoating layer formedon the amorphous structured Co—Cr—Zr alloy layer has (100) orientationand the Co—Cr—Pt magnetic film on the second undercoating layer has(11.0) orientation by the epixial growth. The components of the in-planedirection of the c-axis as an easy axis of magnetization of the Co—Cr—Ptalloy are enlarged and the preferable magnetic characteristics can beobtained.

[0053] When the magnetic film was observed by using the TEM, the averagegrain size of the Co—Cr—Pt alloy of the embodiment 1 was 10.8 nm whichis finer than 16.2 nm of that of the comparison example 1. When themagnetization of the Co—Cr—Zr alloy single layer was measured, a clearhysteresis curve was not obtained. Consequently, it can be consideredthat the alloy layer is non-magnetic.

[0054] <Embodiment 2>

[0055] A magnetic recording medium with a film construction similar tothat of the embodiment 1 was fabricated. A chemically strengthenedaluminosilicate glass of the 2.5 inch type was used as the substrate 40.The first undercoating layers made of 62 at %Co-30 at %Cr-8 at %Ta alloyeach having the thickness of 40 nm were formed on the faces of thesubstrate. The second undercoating layers made of 80 at %Cr-20 at %Tialloy each having the thickness of 25 nm, the magnetic films made of 72at %Co-18 at %Cr-2 at %Ta-8 at %Pt alloy each having the thickness of 23nm, and the carbon protective layers each having the thickness of 10 nmwere sequentially formed. The same single disc process type sputteringapparatus as that of the embodiment 1 was used as a layer formingapparatus and layers were formed in 9 seconds per tact. The argon (Ar)gas pressure at the time of layer formation was fixed to 6mTorr. Theoxygen partial pressure in the main chamber during the layer formingoperation was about 5×10⁻⁹ (Torr).

[0056] The first undercoating layers were deposited in the firstundercoating layer forming chamber in a state where the substrate wasnot heated, heated to 250° C. by a lamp heater in the heating chamber,and exposed to an atmosphere in which 98 mol %Ar-2 mol %O₂ mixed gas wasused and the gas pressure was 4 mTorr (gas flow rate of 8 sccm) forthree seconds in the oxidation chamber, and the layers were sequentiallydeposited. PO₂·t in this instance corresponds to 4 mTorr×0.02×3seconds=2.4×10⁻⁴ (Torr·sec). After forming the carbon protective films,the lubricant films similar to those of the embodiment 1 were applied.

<COMPARISON EXAMPLE 2>

[0057] Comparison example 2 relates to a magnetic recording mediumfabricated under the same conditions as the embodiment 2 except that themixed gas was not introduced in the oxidation chamber.

[0058] The coercive force of the magnetic recording medium of theembodiment 2 was 2,640 oersted which is higher than that of the magneticrecording medium of the comparison example 2 by about 200 oersted. Theproduct Br·t of the residual magnetic flux density Br and the magneticfilm thickness t was 85 gauss micron. v·Isb of the magnetic recordingmedium of the embodiment 2 was 0.98×10⁻¹ ⁵ (emu) which was reduced to54% of 1.81×10⁻¹⁵ (emu) of the magnetic recording medium of thecomparison example 2, so that the medium noise was reduced to almost thehalf of that of the comparison example 2. The reproduction outputs inthe evaluated recording density region of the embodiment 2 and thecomparison example 2 were almost the same. The S/N ratio of the magneticrecording medium was improved by an amount corresponding to thereduction in the medium noise. When the magnetic recording media of theembodiment 2 and the comparison example 2 were actually inserted into amagnetic disk apparatus and recording and reproduction characteristicsby an MR head were evaluated under that conditions of the trackrecording density of 210 kBPI and the track density of 9.6 kTPI. Themagnetic recording medium of the embodiment 2 has an S/N ratio higherthan that of the comparison example 2 by 1.3 times and sufficientlysatisfied the apparatus specification of 2.0 gigabits per square inch ofthe plane recording density. On the other hand, the magnetic recordingmedium of the comparison example 2 had an insufficient S/N ratio andcould not satisfy the apparatus specification.

[0059] <Embodiment 3>

[0060] A magnetic recording medium with a film construction similar tothat of the embodiment 1 was fabricated. A chemically strengthenedaluminosilicate glass of 2.5 inch type was used as the substrate 40. Thefirst undercoating layers made of 85 at %Cr-15 at %Zr alloy having thethickness of 30 nm were formed on the faces of the substrate. The secondundercoating layers made of 80 at %Cr-15 at %Ti-5 at %B alloy eachhaving the thickness of 25 nm, the alloy magnetic film made of 72 at%Co-19 at %Cr-1 at %Ti-8 at %Pt each having the thickness of 22 nm, andthe carbon protective layers each having the thickness of 10 nm weresequentially formed. The same single disc process type sputteringapparatus as that of the embodiment 1 was used as a layer formingapparatus and layers were formed in 8 seconds per tact. The argon (Ar)gauss pressure at the time of layer formation was fixed to 5mTorr. Theoxygen partial pressure in the main chamber during the layer formingoperation was about 3×10⁻⁹ (Torr).

[0061] The first undercoating layers were deposited in the firstundercoating layer forming chamber in a state where the substrate wasnot heated, heated to 240° C. by a lamp heater in the heating chamber,and exposed to an atmosphere in which 79 mol %Ar-21 mol %O₂ mixed gaswas used and the pressure of the mixed gas was 3 mTorr (gas flow rate of6 sccm) for two seconds in the oxidation chamber, and the layers aresequentially deposited. PO₂·t in this instance corresponds to3mTorr×0.21×2 seconds=1.3×10⁻⁴ (Torr·sec). After forming the carbonprotective films, the lubricant films similar to those of the embodiment1 were applied.

<COMPARISON EXAMPLE 3>

[0062] Comparison example 3 relates to a magnetic recording mediumfabricated under the same conditions as the embodiment 3 except that themixed gas was not introduced into the oxidation chamber.

[0063] The coercive force of the magnetic recording medium of theembodiment 3 was 2,680 oersted which is higher than that of the magneticrecording medium of the comparison example 3 by about 200 oersted. Theproduct Br·t of the residual magnetic flux density Br and the magneticfilm thickness t was 69 gauss micron. v·Isb of the magnetic recordingmedium of the embodiment 3 was 0.89×10⁻¹⁵ (emu) which is reduced to 60%of 1.44×10⁻¹⁵ (emu) of the magnetic recording medium of the comparisonexample 3, so that the medium noise was reduced by almost 40% of that ofthe comparison example 3. The reproduction outputs of the evaluatedrecording density region of the embodiment 3 and the comparison example3 were almost the same. The S/N ratio of the medium was improved by anamount corresponding to the reduction in the medium noise. When themagnetic recording media of the embodiment 3 and the comparison example3 were actually inserted into a magnetic disk apparatus and recordingand reproduction characteristics by an MR head were evaluated under thatconditions of the track recording density of 225 kBPI and the trackdensity of 9.8 kTPI, the magnetic recording medium of the embodiment 3had an S/N ratio higher than that of the comparison example 3 by 1.4times and sufficiently satisfied the apparatus specification of 2.2gigabits per square inch of the plane track density. On the other hand,the medium of the comparison example 3 had an insufficient S/N ratio andcould not satisfy the apparatus specification.

[0064] <Embodiment 4>

[0065] A magnetic recording medium with a film construction similar tothat of the embodiment 1 was fabricated. Coating layers of 88 wt %Ni-12wt %P were deposited to the thickness of 13 pm on both faces of thesubstrate made of 96 wt %Al-4 wt %Mg having the outer diameter of 95 mm,the inner diameter of 25 mm, and the thickness of 0.8 mm. The surface ofthe substrate was polished by a lapping machine so that the surfacecenter line average roughness Ra was 2 nm, and is washed and dried.After that, by pressing an abrasive tape against the both of disk facesthrough a contact roll under the existence of abrasive grains whilerotating the substrate by using a tape polishing machine (for example,the one described in Japanese Patent Application Laid-Open No.62-262227), a texture almost in the circumferential direction was formedon the surface of the substrate. Further, dirt adhered onto thesubstrate such as polishing agent or the like was washed away and dried.

[0066] On both of the faces of the substrate processed as mentionedabove, the first undercoating layers made of 60 at %Co-30 at %Cr-10 at%Ta alloy each having the thickness of 20 nm, the second undercoatinglayers made of 85 at %Cr-20 at %Ti alloy each having the thickness of 20nm, the magnetic film made of 72 at %Co-20 at %Cr-8 at %Pt alloy eachhaving the thickness of 20 nm, and the carbon protective layers eachhaving the thickness of 10 nm are sequentially formed, respectively. Thesame layer forming apparatus used in the embodiment 1 was used and thelayers were formed in 9 seconds per tact. The argon (Ar) gas pressure atthe time of layer formation was fixed to 5 mTorr. The oxygen partialpressure in the main chamber during the layer forming operation wasabout 1×10⁻⁹ (Torr).

[0067] The first undercoating layers were deposited in the firstundercoating layer forming chamber in a state where the substrate wasnot heated, then heated to 270° C. by a lamp heater in the heatingchamber, and exposed to an atmosphere in which the pressure of mixed gasof 98 %Ar-2%O₂ was 4 mTorr (gas flow rate of 8 sccm) for three secondsin the oxidation chamber, and the layers were sequentially deposited.This corresponds to 4 mTorr×0.02×3 seconds=2.4×10⁻⁴ (Torr·sec) withrespect to PO₂·t. After forming the carbon protective films, a lubricantobtained by diluting a perfluoroalkylpolyether material with afluorocarbon material was applied as lubricant films.

[0068] In a layer forming apparatus in which the vacuum degree achievedis low and the oxygen partial pressure is large as compared with thelayer forming apparatus used in the embodiments of the invention, or alayer forming apparatus in which time required from the formation of thefirst undercoating layers until the formation of the second undercoatinglayers is long like an apparatus which can form layers simultaneously ona plurality of substrates, it is not necessary to provide the oxidationchamber as in the embodiments, but the fine nucleation by the oxidationcan be derived and effects similar to those of the foregoing embodimentscan be obtained.

[0069] <Embodiment 5>

[0070] A magnetic recording medium with a film construction similar tothat of the embodiment 1 was fabricated. A chemically strengthenedaluminosilicate glass of the 2.5 inch type was used as the substrate. Onthe faces of the substrate, the first undercoating layers made of 60 at%Co-30 at %Cr-10 at %Zr alloy each having the thickness of 25 nm, thesecond undercoating layers made of 85 at %Cr-15 at %Ti alloy each havingthe thickness of 20 nm, magnetic films made of 75 at %Co-19 at %Cr-6 at%Pt alloy each having the thickness of 20 nm, and the carbon protectivelayers each having the thickness of 10 nm were sequentially formed. Anapparatus for forming layers simultaneously on a plurality of substratesheld by a pallet was used as a layer forming apparatus and layers wereformed in 60 seconds per tact. The argon (Ar) gas pressure at the timeof layer formation was fixed to 6 mTorr. The oxygen partial pressure inthe respective chambers during the layer forming operation was about1×10⁻⁸ (Torr).

[0071] The first undercoating layers were deposited in the firstundercoating layer forming chamber in a state where the substrate wasnot heated, then heated to 270° C. by a lamp heater in the heatingchamber, and the layers were sequentially formed. This corresponds toabout 2×10⁻⁶ (Torr·sec) with respect to PO₂·t. After forming the carbonprotective films, a material obtained by diluting aperfluoroalkylpolyether material with a fluorocarbon material wasapplied as lubricant films.

[0072] The evaluation results of the foregoing embodiments andcomparison examples are as shown in Table 2. TABLE 2 First undercoatingPO2 · t vI · sb Hc Br · t layer (Torr · sec) (×10⁻¹⁵ emu) (Oe) (G · μm)Embodiment 60 at % Co- 1.5 × 10⁻⁴ 1.05 2170 88.8 1 30 at % Cr-10 at % ZrComparison 60 at % Co- 3.2 × 10⁻⁷ 2.24 1850 87.0 example 1 30 at % Cr-10at % Zr Embodiment 62 at % Co- 2.4 × 10⁻⁴ 0.98 2640 85.3 2 30 at % Cr-8at % Ta Comparison 62 at % Co- 2.3 × 10⁻⁸ 1.81 2430 84.3 example 2 30 at% Cr-8 at % Ta Embodiment 85 at % Cr-15 at % Zr 1.3 × 10⁻⁴ 0.89 268069.3 3 Comparison 85 at % Cr-15 at % Zr 2.2 × 10⁻⁸ 1.44 2460 66.5example 3 Embodiment 60 at % Co- 2.4 × 10⁻⁴ 0.87 2890 78.3 4 30 at Cr-10at % Ta Embodiment 60 at % Co- 2.0 × 10⁻⁶ 1.12 2090 87.6 5 30 at % Cr-10at % Zr

[0073] When the magnetic films were directly formed, without the secondundercoating layers, on the first undercoating layers made of a Co alloyhaving an amorphous structure or a fine crystal structure which is likethe amorphous structure which was exposed to the oxidizing atmosphere,the magnetic films show a strong orientation (00.1). The orientation issuch that the c-axis of the Co alloy crystal of the magnetic film isoriented to the vertical direction for the film plane. Although themedium cannot be used as an in-plane magnetic recording medium but issuitable to a vertical magnetic recording medium for recording themagnetization in the vertical direction for the film plane.

[0074]FIG. 6 is a schematic plan view of a magnetic disk apparatusaccording to an embodiment of the invention and a schematic crosssection taken on line A-A′. The magnetic disk apparatus comprises: adisc drive mechanism 65 for driving a magnetic recording medium 64 in arecording direction; a magnetic head 61 which is provided so as tocorrespond to the faces of the magnetic recording medium 64 and consistsof a recording part and a reproducing part; a magnetic head drivemechanism 62 for positioning the magnetic head 61 to a desired position;and a read and write signal processor 63 for inputting signals to themagnetic head and reproducing reproduction signals from the magnetichead. By constructing the reproducing part of the magnetic head by a MRhead, sufficient signal intensity in the high recording density can beobtained, so that a very reliable magnetic disk apparatus having arecording density of 1 gigabit or higher per square inch can berealized.

[0075] When the magnetic recording medium of the invention is used inthe magnetic disk apparatus, an interval between two shielding layerssandwitching the magnetic resistive sensor part of the MR head ispreferably 0.35 μm or narrower. When the interval between the shieldinglayers is wider than 0.35 μm, the resolution deteriorates and the phasejitter of signals becomes large.

[0076] Further, the MR head is constructed by a magnetic resistivesensor including a plurality of conductive magnetic layers in whichmagnetization directions are relatively changed by an external magneticfield, thereby causing large resistance change and the conductivenon-magnetic layers arranged between the conductive magnetic layers. Byusing the giant magnetic resistive effect or the spin valve effect, thesignal intensity can be further raised. Consequently, a very reliablemagnetic storage having a recording density of 2 gigabits or more persquare inch can be realized.

[0077] The entire disclosure of Japanese Patent Application No. 8-292451filed on Nov. 5, 1996 including specification, claims, drawings andsummary are incorporated herein by reference in its entirety.

What is claimed is:
 1. A magnetic recording medium comprising: asubstrate; a first undercoating layer made of an alloy including two ormore kinds of elements which oxidize differently formed on thesubstrate; a second undercoating layer directly formed on the firstundercoating layer; and a magnetic film formed on the secondundercoating layer; wherein clusters made of areas rich in the elementswhich are easily oxidized are locally oxidized and are dispersed on aboundary face of the first and second undercoating layers.
 2. A magneticrecording medium comprising: a substrate a first undercoating layer madeof an amorphous alloy including two or more kinds of elements whichoxidize differently formed on the substrate; a second undercoating layerdirectly formed on the first undercoating layer; and a magnetic filmformed on the second undercoating layer; wherein clusters made of areasrich in the elements which are easily oxidized are locally oxidized andare dispersed on a boundary face of the first and second undercoatinglayers.
 3. The medium according to claim 1 , wherein the substrate is aglass substrate.
 4. The medium according to claim 1 , wherein thesubstrate is a substrate made of an aluminum alloy.
 5. The mediumaccording claim 1 , wherein the first undercoating layer is directlyformed on the substrate.
 6. The medium according claim 1 , wherein thefirst undercoating layer is formed on a substrate surface undercoatinglayer formed on the surface of the substrate.
 7. A magnetic storagecomprising: a magnetic recording medium having: a substrate; a firstundercoating layer made of an alloy including two or more kinds ofelements which oxidize differently formed on the substrate; a secondundercoating layer directly formed on the first undercoating layer; anda magnetic film formed on the second undercoating layer; in whichclusters made of areas rich in the elements which are easily oxidizedare locally oxidized and are dispersed on a boundary face of the firstand second undercoating layers; a magnetic head including a recordingpart and a reproducing part, which is provided corresponding to faces ofthe magnetic recording medium; a drive unit for changing relativepositions of the magnetic recording medium and the magnetic head; amagnetic head drive unit for positioning the magnetic head to a desiredposition; and a read and write signal processor for inputting signals tothe magnetic head and reproducing output signals from the magnetic head.8. A magnetic storage comprising: a magnetic recording medium having: asubstrate; a first undercoating layer made of an amorphous alloyincluding two or more kinds of elements which oxidize differently formedon the substrate; a second undercoating layer directly formed on thefirst undercoating layer; and a magnetic film formed on the secondundercoating layer; in which clusters made of areas rich in the elementswhich are easily oxidized are locally oxidized and are dispersed on aboundary face of the first and second undercoating layers; a magnetichead including a recording part and a reproducing part, which isprovided corresponding to faces of the magnetic recording medium; adrive unit for changing relative positions of the magnetic recordingmedium and the magnetic head; a magnetic head drive unit for positioningthe magnetic head to a desired position; and a read and write signalprocessor for inputting signals to the magnetic head and reproducingoutput signals from the magnetic head.
 9. The storage according to claim7 , wherein the substrate of the magnetic recording medium is a glasssubstrate.
 10. The storage according to claim 7 , wherein the firstundercoating layer of the magnetic recording medium is directly formedon the substrate.
 11. The storage according to claim 7 , wherein thefirst undercoating layer of the magnetic recording medium is formed on asubstrate face undercoating layer formed on the surface of thesubstrate.
 12. The medium according to claim 2 , wherein the substrateis a glass substrate.
 13. The medium according to claim 2 , wherein thesubstrate is a substrate made of an aluminum alloy.
 14. The mediumaccording to claim 2 , wherein the first undercoating layer is directlyformed on the substrate.
 15. The medium according to claim 2 , whereinthe undercoating layer is formed on a substrate surface undercoatinglayer formed on the surface of the substrate.
 16. The storage accordingto claim 8 , wherein the substrate of the magnetic recording medium is aglass substrate.
 17. The storage according to claim 8 , wherein thefirst undercoating layer of the magnetic recording medium is directlyformed on the substrate.
 18. The storage according to claim 8 , whereinthe first undercoating layer of the magnetic recording medium is formedon a substrate face undercoating layer formed on the surface of thesubstrate.